[PATCH] x11-servers/xorg-server: modesetting: add support for TearFree page flips

If you experience tearing during scrolling or video display, and
don't find that "install a compositor!" is helpful or fixes the
problem, here's an attached patch against x11-servers/xorg-server
21.1.16.  This backports unreleased X.org support for a "TearFree"
option to the modesetting section of xorg.conf.

Original work by Joshua Stein for OpenBSD.
https://marc.info/?l=openbsd-tech&m=171591279709952

I have updated the patch so it applies to 21.1.16.

I'm _not_ submitting it for inclusion in the port.  This is just
something in my local Git repository that a few people might find
useful.

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de